In the Old West, Lobo Blacke and Quinn Booker confront a killer potion, and a fugitive bent on payback.

In the Wyoming Territory town of Le Four, Lobo Blacke used to be a legendary lawman, until the day an ambush left him confined to a wheelchair. Now he runs a newspaper with onetime New Yorker Booker Quinn, who also helped pen the great man's memoirs. But now Le Four is shaken by rumors that Paul Muller — a bank and train robber whom Blacke helped lock up — might be headed back to town to settle old accounts. And the same week, fourteen people suddenly drop dead after sipping Ozono, a concoction sold by a traveling medicine show. The brew's casualties include the town's sheriff, and without him, Quinn and Blacke must prepare to face the fiendish Muller, and discover the connection between the elixir and the fugitive.